Abstract

In stellar interferometry, image quality improves significantly with the inclusion of more telescopes and the use of phase closure. We demonstrate, using first coherent and then partially coherent white light, a compact and efficient pairwise combination of 12 or more beams. The input beams are lined up and spread through a cylindrical lens into a comb of parallel ellipses, which interferes with a perpendicular copy of itself to form a matrix of interferograms between all pairs. The diagonal elements show interference of each beam with itself, for intensity calibration. The measured white-light visibilities were high and stable.

Figures (7)

Telescope beams are lined up (left) and stretched in the orthogonal direction to form a comb (center). This comb is then interfered with itself rotated at a normal angle. All fringes from all beams are measured on one detector (right).

Laboratory setups: (a) (Laser) binary, a telescope, and a beam combiner: anamorphic optics and a Sagnac 90° shear interferometer. (b) Prismless rotational shear interferometer. One mirror is above the plane of the rest of the elements. (c) White-light source(s), including anamorphic telephoto and the new shear interferometer.

Interference pattern of a single laser beam (“single star,” left) and two lasers (“binary,” right). High-contrast fringes are visible along the diagonal (bottom left to top right), where each beam interferes with itself. For the single star, the contrast remains high, but for the binary, it periodically drops off and rises again with distance from the diagonal. The artificial fringe pattern is a product of the curved wavefront alone. However, the phase of these fringes and their contrast change according to the source and intervening atmosphere.